Is time travel possible? (vis a vis the Grandfather Paradox)

[CraigD]

Though discussion of time machines, and the nature of time and space are pretty fresh, it’s been a while since a serious discussion of the actual possibility or impossibility of time travel graced this forum, so here one (hopefully) goes. (Veterans of such discussions may feel that they’re trapped in some sort of looping causality already, so apologies in advance for any such emotional distress this thread causes)

 

IMHO, the canonic topic for discussion of future -> past time travel is The Grandfather Paradox, which can be stated briefly as:

If you went back in time and killed your grandfather (or grandmother) what would happen?

There are at least the following resolutions to this paradox. All have at least a modicum of theoretical validity.

1. You can try, but you can’t do it (AKA “weak cosmic censoring”). Physical law allows you to go back in time and make the attempt, but an underlying quality of reality (usually described as some related to the collapse of the quantum wave function) prevents you from succeeding at this or any other action that would make it impossible for you to have undertaken your time-trip.
   
2. You can’t even try (AKA “strong cosmic censoring”). Physical law doesn’t allow time-travel into the past, preventing all such paradoxes.
   
3. You can, and *poof* you’re gone as if you never existed (AKA “supertime”). You can do it, and immediately, you cease to ever have exist. You grandparent has still been killed, but by a person who existed only for the interval of time beginning with you target date in the past, and ending with the killing. This resolution requires all sorts of exotic physics to account for a host of conservation of mass/energy violations, implying a sort of higher dimensional “superspace-time”. It gets very weird if someone goes back in time and stops you from doing the killing, etc.
   
4. You can, but before you can do the killing, you alter history so much that you never went back in time. One of myriad variations of #3 that may or may not make you go *poof*.
   
5. You can, and nothing changes. (AKA “many worlds”) You still exist, you remember you grandparent dieing of old age, etc. The universe bifurcates into a different worldline than the one in which you were born. This resolution would constitute experimental proof of the controversial and arguably un-experimentally provable Many Worlds interpretation of Quantum Physics.
   
6. You can, but the result would be terribly strange (AKA “Novikov self-consistency principle”). Strange, strange, strange, but requires no new Physics.
   

Though it’s rather hard to talk hard science on the subject, what are people’s opinions on future –> past time travel? Is there a consensus opinion favoring one of the resolutions above? Or have I omitted a major family of resolutions?

[Jay-qu]

there have been discussed small possibilities of time travel - but in extreme circumstances that dont allow humans to do it. Such as Godel light cones tipping over inside black holes or infinitly long rotating cylinders. These are the result of complex solutions to Eienstiens equations.

[Dark Mind]

Interesting, but I think it belongs in Philosophy of Science... Do you mind if I move it or do you just wanna wait and "see where it goes" before it's moved?

 

I personally don't see much discussion left open with the opening post, just "Do you agree?" and "What are other possibilities?" (<- My main reason for thinking it should be moved).

[Dark Mind]

there have been discussed small possibilities of time travel - but in extreme circumstances that dont allow humans to do it. Such as Godel light cones tipping over inside black holes or infinitly long rotating cylinders. These are the result of complex solutions to Eienstiens equations.

Going back in time requires achieving and exceeding the speed of light. Neither are possible for any known material. And according to Einstein's Theory of Relativity, when matter exceeds the speed of light it becomes *infinitely* expansive (i.e. Bigger than the Universe...) and the amount of energy required is also somewhere around those figures :rolleyes:. Travelling back in time is not a possibility... Right now...

[Jay-qu]

As for the paradox it could also be resolved by considering the possibility of the past not effecting your future. In this idea each instant in time can be considered to be a sheet of paper(crude analogy) and time flows by the transition of moving between the sheets, so if you go into the past (a previous sheet of paper) you will alter that time future but not your own - so you will stay alive and if you return to your time your grandparent will still be alive.

[CraigD]

Interesting, but I think it belongs in Philosophy of Science... Do you mind if I move it or do you just wanna wait and "see where it goes" before it's moved?

I don't mind - I pondered putting it there, but after reading POS’s subtitle (What makes science science?), decided on Physics & Math. That, and the forlorn hope that some brilliant folk might, despite my pessimism, actually be able to make some hard science of the subject.

 

Perhaps a short wait to “see where it goes” is in order.

[Dark Mind]

What if I just leave the redirect in the P&M Forum :hihi:. That way it's essentially in both Forums :rolleyes:.

[Dark Mind]

...But if you just wanna wait and see where it goes, that's fine too. I don't see any real need for it to be in the Philosophy of Science Forum, yet.

[rockytriton]

If you went back and killed your grandfather, you would have never been born and never went back in time to kill your grandfather, so he wouldn't have been killed.

[CraigD]

If you went back and killed your grandfather, you would have never been born and never went back in time to kill your grandfather, so he wouldn't have been killed.

… in which case, you would have been born, and would be free to go back in time and kill you grandfather … etc.

 

This is the loopy essence of the paradox. Like most paradoxes, its contemplation has a certain dizzying appeal.

 

The paradox can be banished by selecting one of several theoretical model. This, IMHO, is where the real fun starts.

[emessay]

1. Does anybody want to compute the total length DNA from the first DNA till current DNA since 3.8 bya? If we assume that a DNA/RNA is 'a byte of conscious life' then it's long long time travel of conscious particle fabric since 3,800,000,000 years ago..............till............conscious human coming.

2. We need to start to analyze from micro-cosmic concious level to understand time-travel from a tiny single cell conscious life. 3.8 bya is well-proven infinite time travel compared with 10,000 yrs our civz.

3. Then we may look real meaning of : backward/forward/accelerated time[ v-->c]

[xersan]

Time travel is possible for past time. You can see the view of thıngs at past. But you cannot any action. You may only see.

[Qfwfq]

Have you found the way to do it Xersan? Can you send information to the past? How do you do it?

[emessay]

Why we should be impatient to answer this, a time travel ? We still do not understand what's really 'Mind' is it ? All of nature of micro-cosmic till macro-cosmic phenomena demonstrate 'master and slave dances' = 'couple dances' = 'galactic dances'.

 

1. Electron as 'slave' for his 'master' of proton.

2. Observable universe mass of all galaxies , I believe also it's just only a 'slave' for his 'master' of total universe energy, galactic-dances phenomena.

3. Space as 'slave' for his 'master' of time required for life existence-needs, till we observe it now after 13.7 bya journey.

4. And finally do we think our mind is only 'a slave' for his master of 'Master-Mind' ?

 

What was happened in 100 billion neuron cells of our nerve system ? Hydrogen-Bond quoted 90% of that working as background [Master] and only 10% we have it as our mind [slave]. But perhaps c.a 70 % : 30 % if we compare our sleeping time 8 hrs : 24 hrs a day-cycle.

I remember Superman film lyric song : " Can you reach My Mind ?"........................

[ldsoftwaresteve]

Allow me to provide a totally different view of this question.

I'm going to come at it from the direction of McCutcheon's theory that says all particles in the universe are expanding at the same rate, constantly. All phenomenon (the detection of a kind of change) are related to the expansion of all particles.

 

That theory effectively says that time travel (backwards or forwards) is not possible without making all particles either contract or expand simultaneously. And if we were somehow able to do that, there isn't any guarantee that we'd have time 'travel'. Causality might not even be in effect if we go backwards (where is the cause of the chicken leg going into my mouth?).

Of course, one is always free to reject a theory. We're just not free of whatever the truth turns out to be.

[xersan]

Have you found the way to do it Xersan? Can you send information to the past? How do you do it?

 

We can see the past.

We can see always the past.

The velocity of light is limited.

The light requires amount of time to travel the distance of things or event.

We cannot see anything simultaneously.

 

When we look at a planet or star by a telescope, the view on ocular (eye-piece) is belonging to the past of star.

 

We can only see.

If we have technology, we can see like “googleearth”.

We can follow the event like a film by seeing.

But I had said, any action or any interference is impossible.

 

 

 

 

 

 

It is useless the discussion with chauvenists

[xersan]

We never send an information to the past. But, we can take a message If it was sent to space in past.

Time travel tales are fiction, not scientific. But, some of mystics likes this. In fact the stories in cinema are impossible.

 

 

It is useless the discussion with chauvenists.